Probe 3 in my Meater test cook had a significantly higher temp than the other probes. I ignored Probe 3 in favor of the readings from other probes, figuring it was either bad probe placement, or an inaccurate probe. Upon removal from the smoker, it was clear that Probe 3 was smack dab in the middle of a layer of fat. Easy to identify once the cook was complete, but hard to identify when the fat is more solid pre-cook. This is why I always cook with at least two probes.
It makes me wonder how many unsuccessful butt cooks are due to probe placement. Resulting in an undercooked butt. It's pretty hard to overcook a butt. On my Meater test cook, I think it would have taken about 4-6 hours to get from 195 (where I took it out) to 205, a range where butt is totally acceptable, and my preference. Lots of wiggle room there. I would never cook to less than 190 (I prefer 195+). Often times when I hear a butt is "dry", the process usually sounds to me like it is in fact undercooked, with the firm texture of undercooked butt being interpreted on the palate as dry. The collagen has not fully converted to gelatin. Gelatin is what makes the butt lip-smackingly moist.